1. Technical Field
This invention relates to polyimide resins which are suitable for use as printed circuit boards, semiconductor package adhesives and encapsulants owing to excellent properties including high bond strength, high reliability and a low modulus of elasticity. It also relates to a method of preparing the same and a composition comprising the same.
2. Prior Art
In accordance with the size reduction and function multiplication of modern electronic equipment, the wiring design for printed circuit boards and semiconductor packages aims at a higher density and further miniaturization. It would be desirable to have as the adhesive used in these applications a low modulus material having high bonding performance, reliability after moisture absorption, compliance with the high-temperature process during mounting, and capability to mitigate the thermal stress upon mounting of electronic components.
Low modulus materials have already been developed in the art by introducing a siloxane structure into polyimides and polyamide-imides which are heat resistant resins. For instance, JP-A 5-009254 and JP-A 6-116517 disclose siloxane-modified polyamide-imides. These resins, however, are insufficiently adherent to copper foil and less resistant to heat. JP-A 10-60111 and JP-A 6-271673 proposes to blend a siloxane-modified polyamide-imide with a compound having at least two maleimide radicals for improving high-temperature properties. The resulting resin composition is less adherent, especially to copper foil. U.S. Pat. No. 5,677,393 (Japanese Patent No. 3,221,756) discloses a heat resistant adhesive film comprising a polyimide silicone having phenolic hydroxyl radicals and an epoxy resin. Since phenolic hydroxyl radicals are located at sterically packed positions and thus hindered from reacting with the epoxy resin, the adhesion effect of hydroxyl radicals arising from the reaction of phenolic hydroxyl radicals with the epoxy resin is not expectable.